Power management control systems including voltage regulators are incorporated within electronic devices to generate a stable output voltage from a varying input voltage supply. The purpose of the voltage regulator is to regulate the external power supplied to the internal circuitry such that the current usage or quiescent power is efficient. The efficiency of battery powered supply systems is directly related to the amount of power dissipated in the voltage regulator.
A particular type of voltage regulator, the low drop out (LDO) linear voltage regulator is used to reduce power consumption by providing the lowest voltage drop across the linear regulator. The lowest voltage drop the regulator can tolerate before loss of regulation occurs is called the “dropout” voltage. As shown in FIG. 1, a linear voltage regulator 10 conventionally includes an amplifier 14 which compares the output of a voltage reference 12 to a sample of an output voltage supplied by feedback elements 24. The output of the amplifier 14 is coupled to a control terminal 16 of a pass element 18 which serves to “pass” current from the unregulated input terminal 20 of the voltage regulator 10, to the regulated output terminal 22 of the voltage regulator 10. The feedback control loop 26 formed by the amplifier 14, pass element 18 and feedback elements 24 acts to force the control terminal 16 of the pass element 18 to a dynamic value that maintains a regulated voltage at the output terminal 22 of the voltage regulator 10.
More specifically, a conventional LDO linear voltage regulator includes a power PMOS pass transistor which substitutes for pass element 18 and a voltage substituting for feedback element 24. An input voltage Vin is applied to the conduction terminal of the PMOS transistor. A parasitic resistance may be serially connected to output capacitance 28. In addition, an optional by-pass capacitance may be connected in parallel to the series RC connection including the output capacitance and the parasitic resistance.
Operation of all integrated circuits (ICs) depends upon a power supply having a potential difference for use in powering internal integrated circuit components to ensure their operation. It is common for the power supply battery to be inadvertently reversed, thereby reversing the bias of the applied potential difference. In the automotive industry, for example, during a jump start, a battery may be mistakenly connected backwards to a circuit wherein the negative supply connects to the positive power rail and the positive supply connects to the negative power rail. As a result, severe damage to integrated circuits connected to the power supply occurs without any form of reverse bias protection between the integrated circuit and the applied potential difference. Moreover, this extreme condition of reverse battery can cause excessive power consumption.
Specifically, many regulators include NMOS devices having intrinsic backgate diodes. When the reverse battery condition occurs, a substantial amount of current will go through the backgate diode and a large amount of power will be dissipated through this device in the regulator.
There, however, are numerous ways that reverse bias protection may be implemented within an integrated circuit design and more particularly within a voltage regulator. Common reverse bias protection circuitry may include current-limiting resistors, diodes or MOS-transistors in series with a big pass transistor.
In many applications where high voltages must be regulated or otherwise controlled in some manner, the circuitry for controlling the high voltages must be constructed to withstand high voltages. The expense, however, of components having high break-down voltages is greater than that of components with lower break-down voltages. In addition, the design that includes high break-down voltage components lack high voltage isolation which is a disadvantage. Thus, there is an advantage in utilizing low break-down voltage components.
Voltage regulators that are designed with low breakdown voltage components, however, cannot be used in high-voltage applications, such as applications that include automotive regulators having a 40 volt power supply.
Although there are many regulators on the market which are operable at a high voltage and provide high precision, there are none that provide an optional mode that includes reverse battery protection.
Thus, there is a need for a low drop-out voltage regulator that may be configurable to provide reverse battery protection circuit and to provide double power density. Moreover, this low drop-out voltage regulator must be operational in high voltage applications.
The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.